Fibre placement tool

ABSTRACT

A fiber placement tool comprising a plurality of tool segments, each tool segment having an outer surface defining a predetermined profile, each tool segment being removably mounted on at least one elongate shaft.

RELATED APPLICATIONS

The present application is based on, and claims priority from, BritishApplication Number 0710832.7, filed Jun. 6, 2007, the disclosure ofwhich is hereby incorporated by reference herein in its entirety.

BACKGROUND TO THE INVENTION

Fibre placement is a method of manufacturing components from compositefibres, such as carbon composite fibre, that involves repeatedly layingdown lengths of the composite fibre onto the outer surface of a tool,referred to herein as a placement tool. The outer surface of theplacement tool defines the shape and configuration of at least onesurface of the component to be formed. The remaining shape andconfiguration of the composite fibre component is dictated by thesubsequent placement of further layers of composite fibre. Common usesof the fibre placement manufacturing method is in the production ofcomposite fibre components within the aerospace industry. For example,this technique is used in the production of long, thin sections ofcomposite fibre such as leading edge spars for helicopter rotor bladesor propeller blades. Equally, this technique is also used in themanufacturer of fuselage sections for commercial passenger aircraft.

During this manufacturing process, the fibre placement tools are mountedwithin a fibre placement machine that as well as being arranged to laydown repeated strips of composite fibre, is also arranged to rotate andotherwise move the fibre placement tool to allow the fibres to be laiddown in the desired precise geometry. The current practice forrelatively long and thin components, such as rotor blade spars, is toform the fibre placement tool from one or more commonly used engineeringmetals. The mass of these metallic placement tools can make themdifficult to control when being rotated by the fibre placement machine,thus limiting both the length and total mass of the composite fibrecomponent being produced. The existing metallic placement tools can alsodeflect under the pressure of the fibre placement head of the placementmachine and also the rotational forces generated, due to their relativelack of stiffness, thus resulting in the programming of the fibreplacement machine having to take this deflection into consideration forthe manufacture of the component within the specified dimensions andtolerances. The relative lack of stiffness of the current metallicplacement tools also limits the length of single component that can bemanufactured using the placement tools, which is an increasingdisadvantage as the range and size and composite fibres increases inmodern aircraft.

Additionally, the existing metallic placement tools tend to bemanufactured as one piece tools. This means that should the design ofthe corresponding component be changed, for example during the overalldesign and development phase of the associated structure, a completelynew placement tool is required. Similarly, in the event of the placementtool being damaged, which can happen from time to time during the fibreplacement process, the entire placement tool must generally be replaced.

It is therefore an object of embodiments of the present invention toprovide a fibre placement tool that allows a greater degree offlexibility in the manufacturer of composite fibre components thanprovided by the existing metallic placement tools.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided afibre placement tool comprising a plurality of tool segments, each toolsegment having an outer surface defining a predetermined profile, eachtool segment being removably mounted on at least one elongate shaft.

Preferably each tool segment includes at least one through hole formedtherein, the through hole extending through the tool segment along alongitudinal axis thereof and having a cross-section corresponding tothe cross-section of at least one of the elongate shaft.

Additionally or alternatively, the fibre placement tool may comprise aplurality of elongate shafts.

The cross-section of at least one of the elongate shafts may benon-circular.

Preferably, the fibre placement tool includes means for securing thetool segments on each elongate shaft.

Preferably, each tool segment may comprises high density foam.Additionally, each tool segment may include at least one reinforcingrib. Additionally or alternatively, each tool segment may comprise anouter layer of composite fibre.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofillustrative and non-limiting example only, with reference to theaccompanying figures, of which:

FIG. 1 shows a fibre placement tool according to an embodiment of thepresent invention;

FIG. 2 shows a cross section through a tool segment according of anembodiment of the present invention;

FIG. 3 shows an enlarged view of one end of a further fibre placementtool according to another embodiment of the present invention; and

FIG. 4 shows a fibre placement tool according to a further embodiment ofthe present invention.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

An embodiment of the present invention is shown in FIG. 1. In theparticular embodiment shown, the placement tool 2 comprises an elongateshaft 4. The elongate shaft 4 may be manufactured from hollow steel orother metal, or may comprise a composite fibre shaft. Placed over theelongate shaft 4 are a plurality of tool segments 6. The combined shapeand profile of the individual tool segments corresponds to the desiredshape and profile of at least a first surface of an elongate componentto be manufactured using the placement tool 2. The number of modulartool segments required for a given individual component will depend onthe component design, shape and the risk associated with design changeduring the development phase of the component design. For example, wherethere is a significant chance that the design of the desired componentwill change during subsequent development, a greater number of toolsegments may be provided, to allow the design changes to be accommodatedby replacing one or more of the tool segments.

Each tool segment 6 has a through hole formed along a longitudinal axisof the tool segment, the cross-section of the through hole correspondingto that of the elongate shaft 4 such that each tool segment can bethreaded onto the elongate shaft 4 to allow the final outer profile ofthe placement tool to be formed by threading the plurality of toolsegments onto the elongate shaft 4. Where a single elongate shaft 4 isused, as illustrated in the embodiment shown in FIG. 1, the individualtool segments may be located with respect to the elongate shaft, andwith respect to one another, by way of a keyway. For example, thecross-section of the elongate shaft 4 may be substantially circular withthe exception of a raised ridge, or key 8, as illustrated in FIG. 2. Thethrough hole in each tool segment will thus include a correspondinglyshaped slot or key way to accommodate the raised ridge on the elongateshaft 4. The raised key thus ensures that all the individual toolsegments are correctly aligned with respect to one another on theelongate shaft 4 and also prevents the unwanted rotation of theindividual tool segments with respect to the elongate shaft. Inalternative embodiments the cross-section of the elongate shaft 4 may beselected so as to automatically restrict how each individual toolsegment can be placed on the shaft 4, for example by providing the shaft4 with an elliptical cross-section thus restricting the number ofpossible orientations of the tool segment with respect to the shaft 2 toand also preventing unwanted relative rotation of the tool segments withrespect to the shaft.

In alternative embodiments a plurality of elongate shafts 4 may beprovided, as illustrated in FIG. 3. In the embodiment shown in FIG. 3,which only shows the end section of corresponding placement tool, theplacement tool comprises two separate elongate shafts 10, 12. This alsoachieves the desired effect of restricting the relative placement of thetool segments on the shafts and prevents the relative rotation of thetool segments with respect to the shafts. The number and size of shaftscontributes to the stiffness of the tool. By optimising the crosssectional areas of each shaft or shafts it is possible to reduce thedeflection of the final tool.

The individual tool segments are held on the corresponding elongateshafts by any suitable means, such as a circlip at each end of theplacement tool or individual circlips at either end of the individualtool segments. Other provisions can be made for restraining the toolsegments on the shaft or shafts which will be readily appreciated bythose skilled in the art, such as for example the use of one or morelocating pins past through and secured to the shafts or the provision ofa threaded section at one or both ends of each shaft and acorrespondingly threaded locknut.

Each individual tool segment 6 is preferably manufactured by machining ahigh density foam block into the desired shape and configuration, but ata nominal thickness below the required final thickness of the toolsegment. Pre-impregnated composite plies are then wrapped around thefoam block to give the desired resultant surface and dimensions of thetool segment, and thus the manufactured component to be formed on thefibre placement tool. However, in alternative embodiments material otherthan high density foam may be used, the only requirement being that thematerial is able to maintain its shape during use. For example, a lightweight metal or metal alloy may be used that could be overlaid with thecomposite plies or may be used as it's surface is produced. In furtherembodiments, individual reinforcing ribs manufactured from a suitablelightweight metal or other material and having a cross-sectioncorresponding to that of the foam blocks may be bonded to either end ofthe blocks prior to the composite fibre being wrapped around the foamblock and the ribs. This is illustrated in FIG. 4, where it can be seenthat each tool segment 6 includes a reinforcing rib 14 at either end ofthe foam block. A certain amount of cross sectional stiffening isprovided from the composite fibres wrapped over the end faces of thefoam blocks (even where no additional reinforcing ribs are used) and,therefore, the carbon fibre end faces may be considered ribs. However,the addition of separate reinforcing ribs bonded at either end of thefoam block may be used to further enhance the stiffness of the resultantstructure.

Also illustrated in FIG. 4 is a further alternative arrangement of theelongate shafts, with three circular shafts being used and beingconfigured such that the individual tool segments can be placed over thethree shafts in only a single configuration.

The use of high-density foam wrapped with composite fibres, inconjunction with an optimised selection of elongate shaft design andnumber of shafts, means that the resulting fibre placement tool has alower mass than a corresponding conventional metallic alternative. Thisallows, on the one hand, the fibre placement tool to be operated athigher speeds and with greater accuracy than with the conventionalmetallic placement tools or, on the other hand, allows individualplacement tools to be manufactured with increased component thickness,length or combination of the two without corresponding increase in mass.With regards to the latter advantage, the increase in stiffness of thefibre placement tools manufactured according to embodiments of thepresent invention, in combination with their lower weight, permit toolsof greater length to be produced in comparison to existing metallictools and thus allow longer components to be produced as single pieces.The use of individual modular tool segments allows individual segmentsto be removed from the shaft or shafts should that segment be damaged insome manner or should be desired to introduce a change to the geometryof the fibre placement tool, for example if the design of the desiredresultant component has changed. As a result, the modular tool segmentsare reusable. With the development of modern aircraft it is highlylikely that such local changes in the tool geometry will be requiredduring the initial stages of manufacture.

Although it has been stated that the preferred material of manufacturefor the individual tool segments comprises high density foam wrappedwith composite fibres, it will be appreciated by those skilled in theart that acceptable performance may still be obtained by using otherlightweight materials. Indeed, the advantages provided by the modulararrangement of the individual tool segments may still be achieved usingconventional metallic machining techniques, although the advantagesgained by decreasing the mass of the fibre placement tool will not beachieved in those particular embodiments.

Further, in some embodiments the arrangement of stiffening ribsextending from a shaft to supporting an outer skin as shown in FIG. 4may be advantageous over conventional metallic tooling techniques evenin applications where a modular tooling arrangement is not required. Thestiffening ribs may be shaped to incorporate the cross-sectional profileof the tool and with the outer surface being defined by a skin whichadopts the rib profile to provide an outer surface having apredetermined profile. The ribs may be suitably distributed along theshaft and their individual profile varied so as to vary the shape of thetool along its length.

1. A method of manufacturing a fibre placement tool, comprising thesteps of: providing at least one elongate shaft; providing a pluralityof reusable tool segments each comprises a high density foam core and anouter layer of composite fibre; forming an outer surface defining apredetermined profile on each of said plurality of reusable toolsegments; forming at least one through hole extending through each ofsaid plurality of reusable tool segments along a longitudinal axisthereof; passing said at least one elongate shaft through said at leastone through hole; and, removing and reusing any one of said plurality ofreusable tool segments as needed.
 2. The method of claim 1, furthercomprising the step of forming a cross section of said at least onethrough hole to correspond to the cross section of the at least oneelongate shaft.
 3. The method of claim 1, further comprising the step ofproviding a plurality of elongate shafts.
 4. The method of claim 1,further comprising the step of providing a means for securing theplurality of reusable tool segments on said at least one elongate shaft.5. The method of claim 1, further comprising the step of providing eachtool segment with at least one reinforcing rib.
 6. The method of claim1, further comprising the step of providing a longitudinal ridge on anouter surface of said at least one longitudinal shaft.
 7. The method ofclaim 6, further comprising the step of providing a longitudinal slotdimensioned and configured to receive said longitudinal ridge on each ofsaid plurality of reusable tool segments.
 8. A fibre placement tool,comprising: at least one elongate shaft; and, a plurality of reusabletool segments, each of said plurality of reusable tool segmentscomprises a high density foam core and an outer layer of composite fibredefining a predetermined profile and at least one through hole formedtherein extending through each of said plurality of reusable toolsegments along a longitudinal axis thereof through which said at leastone elongate shaft passes, each of said plurality of reusable toolsegments being removably mounted on the at least one elongate shaft. 9.A fibre placement tool according to claim 8, wherein the at least onethrough hole has a cross section corresponding to the cross section ofthe at least one elongate shaft.
 10. A fibre placement tool according toclaim 8, wherein the fibre placement tool comprises a plurality ofelongate shafts.
 11. A fibre placement tool according to claim 8,wherein the cross section of the at least one of the elongate shaft isnon-circular.
 12. A fibre placement tool according to claim 8, whereinthe fibre placement tool includes means for securing the plurality ofreusable tool segments on said at least one elongate shaft.
 13. A fibreplacement tool according to claim 8, wherein each tool segment includesat least one reinforcing rib.
 14. A fibre placement tool according toclaim 8, wherein said at least one longitudinal shaft includes alongitudinal ridge on an outer surface thereof.
 15. A fibre placementtool according to claim 14, wherein each of said plurality of reusabletool segments includes a longitudinal slot dimensioned and configured toreceive said longitudinal ridge therewithin.
 16. A fibre placement toolaccording to claim 12, wherein said means for securing said plurality ofreusable tool segments on said at least one elongate shaft is a circlip.